1. Field of the Invention
The present invention relates in general to control systems for controlling internal combustion engines equipped with a variable valve timing mechanism, and more particularly to the control systems of a type which can appropriately control the engine when the variable valve timing mechanism fails to operate normally.
2. Description of the Prior Art
Hitherto, in the field of internal combustion engines, for actuating intake and exhaust valves, various types of variable valve timing mechanisms have been proposed and put into practical use in place of conventional cam type mechanism. Japanese Patent First Provisional Publication (Tokkai) 61-247807 shows a variable type using electromagnetic solenoids, and Japanese Patent First Provisional Publication (Tokkai) 7-317516 shows another variable type using hydraulic actuators. In these variable types, the control for timing the valve opening and closing is carried out without providing the engine with a cam shaft. Japanese Patent First Provisional Publication (Tokkai) 10-47028 shows a measure for dealing with a malfunction of the variable valve timing mechanism which would occur in the type using the electromagnetic solenoids. That is, in the measure, upon detecting a malfunction of the valve actuating mechanism for one cylinder, operation of the intake and exhaust valves of the cylinder is stopped and the amount of air/fuel mixture fed to the remaining cylinders is increased. That is, in such case, operation of the engine is continued by the remaining cylinders.
However, when the engine operates with one cylinder being at rest, smoothed rotation of the engine is not obtained because of lack of balance of the rotation and thus marked vibration of the engine tends to occur. That is, when, upon detecting a malfunction of the variable valve timing mechanism, one cylinder is made inoperative, a torque that is to be produced by the cylinder is not actually produced during operation of the engine. This causes discontinuous production of engine torque and thus brings about the non-smoothed and vibratory operation of the engine.